The present invention relates to a gas laser tube structure, and more particularly to a supporting structure for an end portion of a capillary tube within a gas laser tube.
Among the gas lasers, He-Ne gas lasers have been widely used as a light source for "Point of Sales" equipment, video disk apparatus, etc., because they are compact, light in weight and easy to handle. For such light source use, He-Ne lasers having an output power of 1 mW.about.2 mW are often used, and those having an output power of about 5 mW are also in great demand.
In a He-Ne gas laser tube, as is well known, a laser capillary tube in which a laser medium is produced by discharge, is coaxially disposed within a vacuum envelope containing He and Ne gases, and reflecting mirrors, to be used as a resonator, are disposed on opposite ends of the laser capillary tube. One end of this laser capillary tube is fixedly secured to the vacuum envelope, but the other end is free in order to prevent distortion or damage caused by thermal expansion.
Since the output power of a gas laser depends upon the laser capillary tube length, a laser tube providing a high output power must include a long capillary tube. The capillary tube length of a laser tube of the 1 mW class is about 14 cm, but in the case of a laser tube of the 5 mW class it may be as long as about 30 cm. Since one end of a laser capillary tube is fixed to the envelope but the other end is free as described above, when the capillary tube length is increased, the capillary tube is bent by its weight under gravity. The magnitude of the bending caused by gravity is proportional to a fourth power of the capillary tube length, and hence, a laser capillary tube for a 5 mW laser tube will bend 20 times as much as that for a 1 mW laser tube. If the laser capillary tube bends in the above-described manner, then the light energy propagating back and forth between the reflecting mirrors for laser oscillation will be partly cut off, and as a result, the laser output power will be reduced.
Furthermore, a laser tube including a long capillary tube has the shortcoming that, when the laser tube changes its attitude, the mode of bending of the laser capillary tube is varied, and therefore, the laser output power is varied.
One of the solutions which have been heretofore employed for eliminating the shortcomings of the laser tube having a long capillary tube, such as power reduction and power variation, is the method employed in a 5 mW He-Ne laser oscillator Model 3225H-PC manufactured by Hughes Aircraft Co. in the United States. This method, as will be fully described later with reference to the accompanying drawings, involves a protrusion tube having such an inner diameter that a laser capillary tube may be snugly fitted therein which is projected from the end of the vacuum envelope opposite the end where the capillary tube is fixed and towards the free end of the laser capillary tube; the free end of the laser capillary tube is thus supported by snugly fitting it in the protrusion tube. However, since this method necessitates snug fitting, the manufacture of the laser tube becomes difficult and expensive; furthermore, the thus manufactured laser tube has the shortcoming that unless the snug fitting portion is carefully formed, there exist the possibilities that the fitting portion cannot absorb the elongation of the capillary tube caused by thermal expansion or the laser tube may be damaged by shock and friction.